First Determination of the Weak Charge of the Proton
Bibliographic record
Abstract
The ${Q}_{\mathrm{weak}}$ experiment has measured the parity-violating asymmetry in $\stackrel{\ensuremath{\rightarrow}}{e}p$ elastic scattering at ${Q}^{2}=0.025\text{ }(\mathrm{GeV}/c{)}^{2}$, employing $145\text{ }\text{ }\ensuremath{\mu}\mathrm{A}$ of 89% longitudinally polarized electrons on a 34.4 cm long liquid hydrogen target at Jefferson Lab. The results of the experiment's commissioning run, constituting approximately 4% of the data collected in the experiment, are reported here. From these initial results, the measured asymmetry is ${A}_{ep}=\ensuremath{-}279\ifmmode\pm\else\textpm\fi{}35$ (stat) $\ifmmode\pm\else\textpm\fi{}\text{ }31$ (syst) ppb, which is the smallest and most precise asymmetry ever measured in $\stackrel{\ensuremath{\rightarrow}}{e}p$ scattering. The small ${Q}^{2}$ of this experiment has made possible the first determination of the weak charge of the proton ${Q}_{W}^{p}$ by incorporating earlier parity-violating electron scattering (PVES) data at higher ${Q}^{2}$ to constrain hadronic corrections. The value of ${Q}_{W}^{p}$ obtained in this way is ${Q}_{W}^{p}(\mathrm{PVES})=0.064\ifmmode\pm\else\textpm\fi{}0.012$, which is in good agreement with the standard model prediction of ${Q}_{W}^{p}(\mathrm{SM})=0.0710\ifmmode\pm\else\textpm\fi{}0.0007$. When this result is further combined with the Cs atomic parity violation (APV) measurement, significant constraints on the weak charges of the up and down quarks can also be extracted. That $\mathrm{PVES}+\mathrm{APV}$ analysis reveals the neutron's weak charge to be ${Q}_{W}^{n}(\mathrm{PVES}+\mathrm{APV})=\ensuremath{-}0.975\ifmmode\pm\else\textpm\fi{}0.010$.
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.001 | 0.002 |
| Meta-epidemiology (narrow) | 0.001 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.001 | 0.000 |
| Science and technology studies | 0.001 | 0.001 |
| Scholarly communication | 0.001 | 0.001 |
| Open science | 0.001 | 0.001 |
| Research integrity | 0.001 | 0.001 |
| Insufficient payload (model declined to judge) | 0.002 | 0.001 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".